This invention relates to a wafer processing spin station of the kind in which a wafer is gripped between jaws and is rotated to relatively high speeds of rotation in the course of performing a spinning operation at the spin station.
This invention relates particularly to a wafer processing spin station which has a movable jaw chuck and a balancing mechanism which is effective to maintain the gripping force exerted on the wafer by the movable jaw chuck substantially unaffected by the centrifugal forces developed by the movable jaw chuck during this spinning operation.
Wafers are manufactured with a variety of nominal diameters, such as, for example, 100 millimeters, 125 millimeters, 150 millimeters and 200 millimeters; and each diameter size may have one flat or more than one flat. The angles at which the flats are oriented about the periphery of the wafer also varies.
In order, therefore, for a single machine to be able to perform spinning operations on wafers of more than a single diameter and wafers having other than a fixed number and orientation of flats, the machine must have a jaw arrangement which can accommodate the varied edge configurations of the wafers.
One, or more, of the gripping jaws must be movable to permit the jaws to be moved between an open position for loading and unloading and a closed, clamping position for spinning. A movable jaw must be movable to accommodate the extra travel required when the jaw engages a flat rather than a circular edge of the wafer. A movable jaw must also be able to accommodate a variable amount of offset of the center of a wafer with respect to the axis of rotation of the spin station.
A movable jaw must, as a practical matter, therefore be somewhat adjustable in its final clamping position in order to accommodate varying orientations of flats and varying amounts of offset of individual wafers with respect to the clamping jaws and the axis of rotation.
This variation in final position of a movable jaw element in the clamping position can present problems of balancing the centrifugal force which is developed within the movable jaw element during the rotation required for the spinning operation.
If the centrifugal force is not counterbalanced sufficiently, the movable jaw can move outwardly and release the clamping force on the wafer. This can permit the wafer to fly out of the spin station and to be destroyed.
If the centrifugal force developed by the movable jaw is overbalanced, the movable jaw can be forced inwardly, and the wafer can be crushed.
It is a relatively simple matter to exactly balance the centrifugal force of a movable jaw for any given, exactly known position of the movable jaw. However, because of the practical problem of varying orientations of flats with respect to the jaws and of variation between the amounts of offset of the center of the wafer with respect to the axis of rotation, the final, clamping position of the movable jaw for any particular wafer can't be exactly known. Instead, the clamping position of the movable jaw must be adjustable to accommodate the variation in the amount of travel required from wafer to wafer, and this presents a problem of counterbalancing the centrifugal force developed in the movable jaw in a way that does not let the movable jaw slide out and release the wafer or in a way that does not overcompensate and cause the movable jaw to move inwardly and crush the wafer.